In company with the development of fabrication technology, the current integrated circuits have higher complexity and smaller size compared to the conventional integrated circuits. Therefore, a flip-chip package technology with relatively high integration density and relatively more input/output pins has been developed. The flip-chip package is a technology that can connect semiconductor elements to external circuits. The aforementioned external circuits may include package carriers or printed circuit boards. Compared to other packaging technologies, the merits of the flip-chip package technology include providing more area for input/output connections, reaching relatively high transmission rates with relatively little interference, and preventing interference from the external environmental factors.
The flip-chip package technology uses solder bumps deposited on the chip pads to establish connections to the external circuits. The aforementioned solder bumps are bump pads deposited on the top layer of the wafer in the final wafer fabrication stage. In order to mount the aforementioned chip on an external circuit, the chip is set upside down with its top layer facing down so that the bump pads are aligned with the pads of the external circuit. FIG. 1 shows a flip-chip package. As shown in FIG. 1, a chip 100 is mounted upside down on a package carrier 200. The top layer of the chip 100 has several bump pads 102, which are connected to the package carrier 200 via several solder bumps 104. The chip 100 also has several wire bonding pads or drier pads 106. FIG. 2 shows the cross section of the chip 100. As shown in FIG. 2, in order to lower the circuit design complexity and reduce the design modifications, the chip 100 has an extra metal layer known as a redistribution layer on the top metal layer of the chip 100 to connect the driver pads 106 to the bump pads 102.
Compared to pin grid array or ball grid array routing methods, the routing method for a flip-chip package has more restrictions and must satisfy the design rules of the fabrication process. The routing method for a flip-chip package can be classified into free assignment routing and pre-assignment routing. For the flip-chip package that uses free assignment routing, the corresponding relationships between the driver pads and the bump pads are determined by the user or the routing tool software. Therefore, the user or routing tool software has a relatively high degree of freedom for determining the routing paths between the driver pads and the bump pads. On the other hand, for a flip-chip package using pre-assignment routing, the corresponding relationships between the driver pads and the bump pads are predetermined. Therefore, the corresponding relationships cannot be changed when determining the routing. As a result, routing faces relatively more restrictions because the user or routing tool software can only perform routing according to the predetermined corresponding relationships.
Generally speaking, the difficulty level of a flip-chip package using pre-assignment routing is much higher than that of a flip-chip package using free assignment routing. However, since most of the integrated circuit or package design engineers are used to predetermining the corresponding relationships between the driver pads and the bump pads, and since the routing tool software used in the pre-assignment routing method can also be used to evaluate the aforementioned corresponding relationship, the pre-assignment routing method is still used frequently for the flip-chip package technology in the industrial field.
Currently, there is an integer linear programming algorithm that can be used to calculate the routing paths of a flip-chip package using the pre-assignment routing method. The integer linear programming algorithm includes two stages: in the first stage, the routing path for the connection between each driver pad and its corresponding bump pad is generally determined; in the second stage, details are provided to complete the aforementioned routing paths. However, one of the disadvantages of the integer linear programming algorithm is that it needs a lot of time for the computation. Therefore, the integer linear programming algorithm is unsuitable for the semiconductor field that focuses on efficiency and development costs.
Therefore, the semiconductor field needs a routing method and device for a flip-chip package that can not only efficiently determine the routing path for connection between each driver pad and its corresponding bump pad in the flip-chip package technology, but also reduce the routing length needed.